## pt50 s2 q14

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jlhero

Posts: 49
Joined: Mon Feb 02, 2009 11:52 pm

### pt50 s2 q14

um...

the stem asks of a necessary assumption but the correct answer choice is a sufficient assumption.

the argument has only 1 gap and the gap is bridged perfectly by the correct answer choice.

i am confused.

y could a sufficient assumption be the correct answer choice?

should a necessary assumption only bridge the gap of an argument incompletely?

can someone explain it to me?

thanks~

jlhero

Posts: 49
Joined: Mon Feb 02, 2009 11:52 pm

### Re: pt50 s2 q14

someone please?

suspicious android

Posts: 919
Joined: Tue Feb 09, 2010 4:54 pm

### Re: pt50 s2 q14

Short answer, assumptions can be both necessary and sufficient for an argument's validity. This is not a super common quality for a correct answer on an assumption question, but it does happen. Being sufficient doesn't make it any more or less necessary, they are not mutually exclusive qualities.

Consider the following argument:

Joe is a Texan.
Therefore Joe is an American.

The assumption is obviously "All Texans are Americans", right? Well, that's clearly sufficient, with those two statements the conclusion must be true. However, this assumption is also necessary for the argument, since without it, we have no basis for the conclusion.

Basically if you are looking for a necessary assumption, an answer choice being sufficient should not affect your decision about its suitability.

jlhero

Posts: 49
Joined: Mon Feb 02, 2009 11:52 pm

### Re: pt50 s2 q14

thanks,

but can u consider this example?

A beer costs \$2, and X has enough money to buy a beer.

if u assume X has exactly 2 dollars, it is a sufficient assumption but it is not a necessary assumption.

a necessary assumption would be something like, x has at least 1 dollar.

KevinP

Posts: 1322
Joined: Sat Sep 26, 2009 8:56 pm

### Re: pt50 s2 q14

jlhero wrote:thanks,

but can u consider this example?

A beer costs \$2, and X has enough money to buy a beer.

if u assume X has exactly 2 dollars, it is a sufficient assumption but it is not a necessary assumption.

a necessary assumption would be something like, x has at least 1 dollar.

Correct in that if X has exactly 2 dollars, the condition is a sufficient, but not a necessary condition. This is attributed to the keyword exactly; X is not required to have exactly 2 dollars since X could just as well have 3 dollars.

However, if you have the condition that X has at least 2 dollars, then that is both a sufficient and a necessary condition.

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